The invention relates to a machine for wrapping commodities of substantially parallelepiped shape, and in particular, a machine serving to envelop such parallelepiped items in an outer wrapping of transparent material.
The prior art embraces machines for placing an outer wrapping around parallelepiped commodities, especially packs of cigarettes (the case to which the following specification refers); such machines comprise a head, or wheel, rotatable intermittently about a horizontal axis and affording peripheral radial pockets spaced apart one from the next at identical angular distances, each of which designed to accommodate one pack of cigarettes.
The single pocket comprises a bottom wall, nearest the center of the wheel, two substantially radial walls set apart one from the other at a distance essentially matching that of the thickness of one pack, and two end walls embodied generally as two blades or tongues occupying planes normal to the axis of the wheel, located one on either side and separated by a distance corresponding substantially to the longitudinal dimension of the finished paok.
During each pause produced by intermittent rotation of the wheel, one of the pockets comes to rest at an entry station, in alignment with a reciprocating push rod; stroking forward, the rod engages one pack of cigarettes from the rear flank (considered in relation to the path of entry) and directs it into the waiting pocket together with the wrapper, which consists in a single sheet of material fed through a vertical plane transversely to the path of the entering pack.
On completion of the push rod stroke, the pack will be fully inserted in the pocket with its leading flank flush against the bottom wall.
During the course of this operation, the wrapper is folded gradually into a U shape around the pack, enveloping it on three sides.
The transverse dimension of the wrapper, as seen in relation to the direction of entry, is such that its two sides project a given distance beyond the longitudinal dimension of the pack.
On insertion of the pack into the pocket, these projections will be engaged by the leading edges of the blades aforementioned, and folded in part to envelop a proportion of the two faces of the pack normal to the wheel, i.e. the end faces.
Likewise, the longitudinal dimension of the wrapper is such that, when folded into the U formation, the relative ends project beyond the peripheral limit established by the two radial walls of the pocket.
These two projecting ends, or flaps, are folded subsequently, the one by a moving element traversed across the entry point, and the other by a fixed element forming part of a cowling coaxial with the wheel, which engages the corresponding part of the wrapper as the wheel is set in rotation.
With the two radial flaps folded and overlapping, and the wrapper enveloping the pack essentially in tubular fashion, the flank of the pack positioned outermost is offered to a heat-seal device located at a further station subsequently to be occupied by the indexing pocket, and the overlapping flaps are fused together.
With the pack enveloped thus far by the transparent wrapper and entirely encompassed by the wheel and cowling with the exception of the two small end faces, the pocket is indexed ultimately to an exit station diametrically opposed to the entry station, where a further reciprocating push rod proceeds to eject the pack from the wheel, directing it forward into a runout channel along which the operations of folding and sealing the ends of the wrapper will be brought to completion.
Given that the first sealing device in conventional machines serves only to fix the overlapping parts of the two longitudinal flaps that are effectively breasted with the corresponding flank of the pack, it follows that the sealing device installed along the runout channel must, at a single stroke, secure not only the two sets of end flaps gathered up and flattened in the subsequent folding operations, but also the remaining and as yet unsealed end parts of the longitudinal flaps.
In a typical parallelepiped pack as turned out by the conventional machine described above, each end fold comprises six overlapping layers; accordingly, the duty performed by the second sealing device in securing these folds is somewhat heavy, especially where the transparent wrapping material utilized happens to be relatively thick, and in practice the outer wrappings of cigarette packets are often less than perfectly sealed.
The object of the present invention is to embody a wrapping machine capable of overcoming the drawback discerned in the prior art and outlined above, in short, a machine capable of effecting a faultess seal in the transparent wrappings of substantially parallelepiped commodities.